﻿38 
  Prof. 
  Ohattock 
  and 
  Mr. 
  Tyndall 
  on 
  Changes 
  

  

  originally 
  in 
  the 
  hydrogen 
  ; 
  the 
  volume 
  of 
  the 
  oxygen 
  being 
  

   of 
  course 
  measured 
  at 
  the 
  same 
  temperature 
  and 
  pressure 
  as 
  

   the 
  hydrogen 
  with 
  which 
  it 
  was 
  afterwards 
  mixed. 
  The 
  

   volume 
  of 
  the 
  discharge 
  vessel 
  alone 
  (136 
  c.c.) 
  was 
  used 
  in 
  

   calculating 
  v 
  Q 
  as 
  the 
  oxygen 
  in 
  the 
  space 
  above 
  the 
  gauge 
  

   was 
  not 
  affected. 
  

  

  The 
  mean 
  value 
  of 
  v/v 
  Q 
  is 
  thus 
  2*8 
  ; 
  and 
  this 
  agrees 
  with 
  

   another 
  value, 
  2*7, 
  obtained 
  from 
  air, 
  on 
  the 
  assumption 
  that 
  

   the 
  oxygen 
  alone 
  combines 
  with 
  the 
  hydrogen 
  in 
  this 
  case 
  

   (for 
  justification 
  of 
  this 
  see 
  below). 
  

  

  For 
  both 
  air 
  and 
  oxygen 
  the 
  ratio 
  is 
  a 
  little 
  larger 
  for 
  

   negative 
  than 
  for 
  positive 
  discharge, 
  but 
  the 
  agreement 
  

   between 
  the 
  individual 
  values 
  is 
  not 
  good 
  enough 
  to 
  warrant 
  

   the 
  conclusion 
  that 
  this 
  difference 
  is 
  real. 
  

  

  Now, 
  as 
  already 
  explained, 
  the 
  water- 
  vapour 
  formed 
  may 
  

   be 
  taken 
  as 
  having 
  remained 
  in 
  the 
  discharge 
  vessel 
  during 
  

   the 
  quarter 
  of 
  an 
  hour 
  of 
  the 
  discharge 
  and 
  subsequent 
  drift 
  

   readings 
  ; 
  and 
  this 
  means 
  that 
  if 
  the 
  combination 
  occurring 
  

   was 
  that 
  of 
  gaseous 
  hydrogen 
  and 
  oxygen 
  the 
  value 
  of 
  v/v 
  

   should 
  be 
  not 
  greater 
  than 
  1, 
  even 
  if 
  the 
  whole 
  of 
  the 
  oxygen 
  

   combined. 
  

  

  The 
  discrepancy 
  seems 
  to 
  us 
  to 
  be 
  connected 
  with 
  the 
  

   position 
  of 
  the 
  combination 
  region. 
  On 
  this 
  head 
  we 
  hope 
  to 
  

   have 
  more 
  to 
  say 
  in 
  a 
  later 
  paper, 
  but 
  some 
  evidence 
  has 
  

   already 
  been 
  obtained 
  which 
  points 
  to 
  a 
  gas 
  film 
  on 
  the 
  

   surface 
  of 
  the 
  electrode 
  as 
  the 
  seat 
  of 
  at 
  least 
  a 
  large 
  part 
  

   of 
  the 
  chemical 
  action. 
  If 
  this 
  turns 
  out 
  to 
  be 
  correct, 
  it 
  

   may 
  well 
  happen 
  that 
  the 
  water- 
  vapour 
  formed 
  gets 
  entangled 
  

   in 
  the 
  film 
  for 
  so 
  long 
  that 
  when 
  it 
  does 
  evaporate 
  the 
  

   change 
  of 
  pressure 
  is 
  reckoned 
  in 
  with 
  the 
  general 
  drift 
  of 
  

   the 
  pressure-gauge 
  and 
  does 
  not 
  appear 
  in 
  p. 
  This 
  would 
  of 
  

   course 
  result 
  in 
  the 
  value 
  3 
  for 
  v/v 
  if 
  no 
  oxygen 
  is 
  left 
  

   uncombined 
  at 
  the 
  drop. 
  If 
  10 
  per 
  cent, 
  is 
  left 
  uncombined 
  

   the 
  ratio 
  should 
  be 
  2*7, 
  and 
  this 
  is 
  almost 
  exactly 
  the 
  mean 
  

   value 
  of 
  all 
  the 
  oxygen 
  and 
  air 
  determinations 
  *. 
  

  

  The 
  interpretation 
  of 
  the 
  ratio 
  found 
  is 
  almost 
  sure 
  to 
  be 
  

   interesting, 
  and 
  light 
  would 
  probably 
  be 
  thrown 
  on 
  it 
  if 
  we 
  

   could 
  get 
  its 
  value 
  for 
  much 
  higher 
  percentages 
  of 
  oxygen 
  ; 
  

   but 
  the 
  labour 
  would 
  be 
  too 
  great 
  to 
  face 
  with 
  the 
  present 
  

   apparatus. 
  To 
  clear 
  out 
  5 
  per 
  cent, 
  would 
  take 
  about 
  500 
  

   hours. 
  With 
  a 
  discharge 
  vessel 
  one-fiftieth 
  the 
  present 
  size 
  

   large 
  percentages 
  could 
  be 
  used, 
  and 
  with 
  these, 
  as 
  well 
  as 
  

  

  * 
  Hydrogen 
  in 
  contact 
  with 
  phosphorus 
  pentoxide 
  contains 
  about 
  

   0-00002 
  per 
  cent, 
  by 
  weight 
  of 
  the 
  latter 
  (Morley, 
  J. 
  Am. 
  Chem. 
  Soc. 
  

   xxvi.), 
  but 
  this 
  is 
  far 
  too 
  small 
  a 
  quantity 
  to 
  account 
  for 
  the 
  high 
  ratio 
  by 
  

   combining 
  with 
  the 
  water-vapour 
  formed. 
  

  

  